Fuse link



R. H. EARLE June'lo, 1941.

FUSE LINK Filed March 20, 1939 INVENTOR.

ATTORNEY.

Patented June 10, 1941 1 I FUSE LINK Ralph H. Earle, Wauwatosa, Wis., assignor to Line terial Company, South Milwaukee, corporation of Delaware Wis., a

Application March 20, 1939, Serial No. 262,932

22 Claims. This invention relates to improvements in fuse nks Fractional ampere fuse -links are preferably .placed under tension in order to Ainsure wide separation of the fused portions of the link when the fusible section is ruptured, but owing to the extreme tensile weakness of the fusible section,

it is necessary to avoid placing any tension thereon and to provide means operable when the fusible section ruptures to release the tensioned portions'of the fuse link for movement of the fused portions away from and out of all mechanical connection with each other, thereby to avoid leakage across the link that might otherwise occur. I.

Accordingly. it is an object' of this invention' to provide a fractional ampere fuse link con.- struction in which the mechanical forces set up by a tensioning spring will be imposed upon relatively insulated conducting parts of the fuse link, rather than the fusible section, the conducting parts of the link being released for relative movement, upon the establishment of an arc between them, by the spring when the fusible section is ruptured.

More specifically, it is an object toprovide for expulsion fuses a fractional ampere fuse link having mechanically connected insulated conductive portions, terminal portions mechanically connected with the insulated conductive portions and normally in non-conductive relationship, at least one of the conductive portions'being destructible under the influence of an arc established between them, a mechanically Weak fusible element electrically connecting the terminal portions, and tensioning means for separating the terminal portions when the fusible element is ruptured and an arc is established.

In the drawing:

Fig. 1 shows a view in side elevation, partly in section, showing a fuse link embodying this invention mounted in a fuse cartridge.

Fig. 2 shows an enlarged sectional view of the fuse link shown in Fig. 1.

Fig. 3 shows a view in in section, showing a modified form of fuse link embodying this invention and mounted in a fuse cartridge of standard design.

. Fig. 4 shows an enlarged sectional fuse link -shown in Fig. 3.

Fig. 5 shows another modified form of fuse link embodying this invention.

Fig. 6 shows an enlarged side View of the inside elevation; partly View of the sulator pin support used in the fuse link shown in Fig. 5. l

Fig. 7 shows an end view illustrated in Fig. 6.

In Fig. 1, the fuse cartridge A comprises an outer tube I of any suitable insulating material of the pin support having an inner fibre tube 2. The cartridge A is closed at its upper end by means of a contact ferrule 4 which is removably threaded on the outer tube I. Threadedly mounted on the lower open end of the tube I is a cylindrical contact ferrule 5 having an inner apertured ange Il intermediate its ends engaging `the lower ends of the tubes I and 2. As indicated, the opening 6 in the flange II leaves the bore 8 of the cartridge A unobstructed. Threadedly mounted on the lower end of the ferrule 5 and engaging the flange II is a spring housing or tube 'l made of any suitable insulating material.

'I'he fuse link B, shown in greater detail in Fig. 2, comprises a metallic contact cap I Z having a centrally-disposed aperture I6 and a tubular shank I3 integral therewith. A metal sleeve I4, comprising a conductor under predetermined conditions, is mounted on the shank I3 and secured thereto by punching as at I5 or another suitable manner. The lower portion of the sleeve is provided with diametrically-aligned openings I9. A bre tube Il is mounted within the sleeve I4 in abutting relationship to the lower end of the shank I3 and is provided with diametricallyaligned openings I8 coaxial with the openings I9.

A tubular insulating support or pin 26 made of any suitable insulating material, such as porcelain, is inserted in the apertures I8 and I Il. A strain wire 23, having a loop 24 which receives the pin 26, extends from the tube Il and ter- .minates in a hook 25 remote therefrom. A conducting rod 21 is secured to the lower portion ofthe strain wire 23 by means of a clamping collar 28 which is prevented from leaving the strain wire by thehook 25. A fibre tube 29 is mounted on the end of the fibre tube I1 which projects from the sleeve I4 and surrounds the strain wire 23 and its connection with the rod 27.

The structurethus far described will not, except under abnormal conditions as will hereafter appear,conduct current because the pin 26 insulates the strain Wire 23 from the metal sleeve I4. However, to render the link conductive, a fine fusible wire 20 is secured at 2I in the aperture I6 in the contact cap I2 and extends to the clamping sleeve 28 where it is secured to the rod 21.

The fuse wire 20 comprises two wires, one of which extends from 'the collar 28 to a point immediately above the pin 26, and the other of which 20B of greater conductive capacity is located below the pin 26. In this manner fusing of the wire 28 is localizedto a point above the pin 2S.

A brous material 22, such as glass or rock wool, or any similar material having similar characteristics, is packed around the fuse wire 28.

An important function of the material 22 is to ysupport the fuse wire, thereby preventing vibratio`n and other disturbances of the wire which may change its characteristics.v

The link B is mounted in the cartridge A, as shown in Fig. l, after removing the contact ferrule, by inserting the link into the bore of the tube A at the upper end of the cartridge. The ferrule is then threadedly mounted on the cartridge and firmly clamped to thecap I2 to secure electrical contact therewith. When the link is thus mounted, the rod 21 extends into the tube 1 to a point adjacent the open end of the cartridge. A spring 32, mounted within the tube 1 and provided with a cupped washer 33 at itslower end, is held under compression, with its upper end in contactwith the flange II, by means of the rodl 21, the lower end of which passes through the aperture 36 in the washer 33 and is hooked at 35 for engagement with the washer.

When a predetermined overload current occurs in an electrical circuit including the fuse link B, the fusible section 28C melts and an arc is established between the shank I3 and the loop 2Q.' which, under given overload conditions, will cut the loop, whereupon the spring 32 'will expel the rod 21 and strain wire 23 from the tube 29. If the excess voltage in the circuit is not suilicient to maintain this arc until the loop is severed, but is still in excess above normal voltage, an arc will be established in the shorter path through the apertures I8 and i9 and between the sleeve It and the strain wire loop 24. Then this arc thus established quickly cuts the loop 24 and thereby renders the loop ineffective to hold the spring 32 under compression. Thereupon the spring operates to withdraw the rod 21 and the severed strain wire 23 from the cartridge.

Fig. 3 shows a cartridge C comprising an electrically non-conductive tube 31, an upper tubular contact or ferrule 38 mounted on the upper end of the tube 31, a closure cap 39 threadedto the ferrule 38, and a lower contact or sleeve 40 secured to the lower portion of the tube 31. The lower contact is provided with a link-engaging clamping bolt 4I threaded into the boss 42' on the terminal 40, the boss being slottedtransversely A strain wire 58 is provided at its upper end with'a loop 55 through which a supporting pin 51, preferably of insulating material. is inserted. As indicated, the pin 51 is suiiiciently long to rest on the shoulder 52 and prevent withdrawal of the strain wire 54 until released as hereinafter set forth.

The lower portion of the fuse wire 48 is electrically connected in any suitable manner, as by soldering, directly to the conductor rod 58. The lower portion of the strain wire 54 is secured in the conductor rod 58 by means of an indented portion of the rod as indicated at 59. Surrounding the rod 58, is a coil spring 6I engaged at one end with the lanchor spur 6l! and at the other end. with a ferrule 62 threaded on the convolutions of the spring. The ferrule 62, by reason of its engagement with the lower end of the fibre tube 53, cooperates with the pin 51 acting through the strain wire 54 to normally maintain the spring 6l expanded, thereby tensioning the strain wire.

lThe rod 58, when released in the manner hereinafter described, is freely slidable through the ferrule 62 under the urge of the spring 6I and is secured at its lower end to a exible leader 43 by means of a deformed collar 86.

The fuse wire i8 is similar to the fuse wire 20 shown in Fig. 2 with a conducting portion 48B comprising electrically parallel wires which in effect locate the fusible section 58C between the cap 65 and the loop 55.

The fuse link D is inserted in the upper end of the cartridge C after removal of the cap 39. The cap 39 is then replaced to firmly clamp the link cap 65 on the end of the ferrule 38, and the flexible leader 43 is drawn around the open end of the cartridge and secured to the boss 42 by the thumb screw ill.

When a predetermined overload occurs in a circuit including the link D, the fusible section 58C melts and an are is established between the cap t5 and the loop 55, which, under given overload conditions, will sever the loop, whereupon the spring 6I operates to withdraw the rod 58 and strain wire 54 from the tube 5U and projects them with the exible leader 43 from the cartridge C. vIf the excess voltage in the circuit is not sufficient to maintain this arc until the loop is severed, then an arc will be established in the shorter path through the aperture 5I between the indent 66 of the sleeve 46 and the loop 55 of the strain wire 55. The arcing set up at this point severs.the wire and the spring 6I operates in the same manner as described heretofore.

The description of the fuse link shown in Fig. 2 will apply to substantiallyl the entire structure shown in Fig. 5, except that the fibrous material 22A may be impregnated with' a metallic salt such as potassium chromate or anyother comminuted substance, preferably non-corrosive. to

f insure the establishment of an arc from the relative to the bolt 4I to receive the flexible leader 43 of the fuse link D. The fuse link D is shown in greater detail in Fig. 4, wherein it comprises a contact cap 45 reduced bore portion .53 forming a shoulder-like support 52. The tube 50 is retained in the sleeve 46 by means of lndents 66 projecting into the apertures or openingsSI. l

shank I3 to the loop 24 when the -fusible section 20C melts because of an overload current in the circuit. The pin 26, shown in Fig. 5, is provided with a pencil-like line 68 of graphite or similar current-conducting material extending from one end to the other. This pencil-like line serves as a means to effect establishment of an arc between' the sleeve I4 and the loop 24 in case the excess voltage in the circuit is not sufllcient to maintain the varc from the shank I3 through the impregnated material 22A to the loop 2'4 long enough to insure destruction of the loop.

Figs. 6 and '1. show a modification of the insulating tube or pin 28 shown in Fig. 5. In this ystroy the loop.

modification, the pin is provided with a groove 69 extending from one end to the other and filled with a compact resistance material, such as graphite, adapted to establish an arc between the sleeve I4 and the loop 24 when the excess voltage in the circuit is not suiiicient to maintain the -arc from the shank I3 to the loop 2l and thereby de- It becomes apparent from the foregoing description that a fractional ampere link has been provided which prevents all destructive mechanical stresses from being imposed upon the fusible portion; insures the establishment of an arc between parts of a link, at least one of which is destructible under the inuence of the arc; and which positivelyseparates the fused parts of the fusibleportion when the arc has been established.

I claim:

1. A fuse link comprising a terminal, an electrically conductive sleeve secured to said terminal, an insulating sleeve within said conductive sleeve, said sleeves each having diametricallydisposed aperatures coaxial with the apertures of the other sleeve, an insulating pin extending diametrically across said sleeves and disposed in said apertures, a strain wire looped about said pin and disposed Within said insulating sleeve, a conductor mechanically connected to said `strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, said sleeves, pin, and strain wire preventing mechanical stresses from being transmitted to said fusible wire.

2. A fuse 'link comprising a tubular terminal member, an electrically conductive sleeve secured to said terminal member, an insulating sleeve within said conductive sleeve, said sleeves each having diametrically-disposed apertures coaxial with the apertures of the other sleeve, an

insulating pin extending iianietrically across said sleeves and disposed in said apertures, a strain wire looped about said pin and disposed within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire extending through said tubular terminal and electrically secured thereto and electrically connected with said conductor.

3. A fuse link comprising a terminal including an electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve having diametrically-disposed apertures within said conductive sleeve', a strain pin extending diametrically across said insulating sleeve and held against longitudinal motion relative thereto, a strain wire looped about said pin and disposed within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire elec- I trically connecting said terminal and conductor, f

the looped kportion of said strain wire being adjacent said apertures, whereby when said fuse wire is ruptured an arc will be established through at least one of said apertures between -said loop and conductive sleeve.

4. A fuse link comprising a terminal including said strain wire. and a mechanically weak fusible wire 'electrically connecting said terminal and conductor, the looped portion of said strain wire being adjacent said apertures.

5. A fuse link coxncprising a terminal member, an electrically onductive sleeve secured to said terminal member, an insulating-sleeve within said conductive sleeve, said sleeves'each having diametrically-disposed apertures coaxial with the apertures of the other sleeve, an insuvlating pin extending diametrically across said an electrically conductive sleeve secured to saidterminal member, an insulating sleeve within said conductive sleeve, said sleeves each having diametrically-disposed apertures coaxial with the apertures of the other sleeve, said insulating sleeve and terminal member having a non-conductive fibrous material contained therein, an insulating pin extending diametrically across said sleeves and disposed in said apertures and acting as a support to said fibrous material, a strain wire looped about said pin and disposed within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor and held in suban electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve having diametrially disposed apertures, said conductive sleeve having indents projecting into said apertures and retaining the insulating sleeve within said conductive sleeve, a strain pin extending diametrlcally across said insulating sleeve and heldagainst longitudinal motion relative thereto, a strain wire looped about said pin, a conductor `mechanically connected to insulating sleeve and stantially rigid position by said material, the

looped portion of said strain wire being adja-v cent said apertures.

7. A fuse link comprising a terminal including an electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve having diametrically-disposed apertures, a strain pin extending' diametricaliy across said insulating sleeve, a strain wire looped about said pin. a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, the looped portion of said strain wire being positioned relative to said apertures so that an arc may be established between said loop and said conductive sleeve when said fusible wire is destroyed by a predetermined overload.

8. A.A fuse link comprising a terminal includinsulating sleeve having diametrically-disposed apertures, said conductive sleeve having indents i projecting into said apertures and' retaining the insulating sleeve within said conductive sleeve, a strain pin extending diametrically across said supported thereinby shoulder means disposed below said apertures, a strain wire looped about said pin, .a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connectlngsaid terminal and conductor.

9. A fuse link comprising a terminal including A an electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve being apertured radially, a strain pin extending diametrlcally across said insulating sleeve, a strain wire looped about said pin, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, the looped portion of said strain wire being positioned relative to the apertured portion of said insulating sleeve whereby a minimum distance. between said loop and said conductive sleeve is obtained. V

l 10. Afuse link comprising a terminal member, anelectrically conductive sleeve secured to said terminal, an insulating sleeve within said conductive sleeve, each of said sleeves being apertured radially, an insulating pin extending diametrically across said insulating sleeve, said pin being provided with an arc-directing substance on the surface thereof, a strain wire looped about said pin, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, the looped portion of said strain wire being positioned relative to said .substance in order to be destroyed by an arc directed thereto.

ll. A fuse link comprising a terminal member including an electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve being apertured radially, la strain wire secured in said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanicallyvweak fusible wire electrically connecting said terminal and conductor, the strain wire being positioned relative to the apertured portion of said insulating sleeve whereby it may be destroyed by an arc directed thereto through said apertured portion.v

12. A fuse link comprising a terminal member including an electrically conductive sleeve, an insulating sleeve within said conductive sleeve, said insulating sleeve being apertured radially whereby a conductive means may be received therein, an insulating support disposed within said insulating sleeve, a strain wire secured to said support within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, the strain `wire being positioned relative to the apertured portion of said insulating sleeve whereby it may be destroyed by an arc directed thereto from said means.

13. A fuse link comprising a terminal member including an electrically conductive means, a mechanically weak fusible wire, an insulating sleeve being apertured radially and having a support secured therein against withdrawal, a strain wire secured within said sleeve, a conductor mechanicallyconnected to said strain wire, said conductor connecting said terminal and extending into the apertured portion of said sleeve and acting as an anchor, the strain wire being positioned relative to the apertured portion of said sleeve whereby it may be destroyed by an arc directed thereto from said anchor.

i4. A fuse link comprising a terminal member, an electrically conductive sleeve securedl to said terminal, an .insulating sleeve within said conductive sleeve. each of said sleeves being apertured radially, an insulating pin extending diametrlcall'y across said sleeves, a "strain `wire looped about said pin and disposed within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminal and conductor, said insulating sleeve and terminal member havinga metallic salt contained therein to insure the establishment of an arc between said terminal and conductor when said fusible wire is destroyed by a predetermined overload.

15. A fuse link comprising a terminal member, an Ielectrically conductive sleeve secured to said terminal, an insulating-sleeve within said conductive sleeve, each of said sleeves being apertured radially, an insulating pin extending diametrically across said sleeves, a strain wire looped about said pin and disposed Within said insulating sleeve, a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire electrically connecting said terminalv and conductor, said insulating sleeve having a non-conductive brous material contained therein'and impregnated with potassium chromate thereby to insure the establishment of an arc between said terminal and conductor when said fuse wire is destroyed by a predetermined overload.

16. A fuse link comprising a terminal, an electrically conductive sleeve secured to said terminal, an insulating sleeve within said conductive sleeve, said sleeves each having diametrically disposed apertures coaxial with the aperturesoi pin and disposed within said insulating sleeve,

a conductor mechanically connected to said strain wire, and a mechanically weak fusible wire connected to said terminal and to said conductor at a point remote from said pin, said sleeves, pin, and strain wire preventing mechanical stresses from being transmitted to' said fusible wire.-

17. A link for connecting electrical terminals, said' link comprising a terminal, an electrically conductive sleeve secured Ato said terminal, an insulating sleeve Within said conductive sleeve, said insulating sleeve having a radially disposed aperture, an insulating pin in said insulating sleeve, saidy insulating sleeve including means holding said pin against withdrawal therefrom adjacent said aperture, a strain wire looped about said pin, a conductor mechanically connected to said strain wire and extending'from the insulating sleeve,-and an electrically con. ductive securing means extendingfrom said electrically conductive sleeve into said aperture, whereby to secure said sleeves against relative movement. g

18. A link for connecting electrical terminals. said link comprising a terminal, an electrically conductive sleeve secured to said terminal, an insulating sleeve within said conductive sleeve. said insulatingsleeve having a radially disposed aperture, an insulating pin insaid insulating sleeve, said insulating sleeve including means holding said pin against withdrawal therefrom adjacent 'said aperture, a strain wirel looped about said pin, a conductor mechanically connected tov said strain wire and extending from the insulating sleeve, and a mechanically weak fusible wire electrically connecting said terminal' and conductor.

' radially extending aperture, a strain pin disposed in and extending across said insulating sleeve and held against withdrawal from said from said insulating 20. A link for connecting electrical terminals,v

sleeve and adjacent said aperture, a strain wire looped about said pin, and a conductor mechani` cally' connected to said strain Wire and extending sleeve,

said link comprising a terminal, an electrically conductive sleeve secured to said terminal, an insulating sleeve xedly secured within said conductive sleeve, said insulating sleeve having a radially extending aperture, a strain pin disposed in and extending across said insulating sleeve and held against withdrawal from said sleeve and adjacent said aperture, a strain wire looped about said pin, and .a mechanically Weak fusible wire electrically connecting said terminal and conductor.

21, A link for connecting electrical terminals, said link comprising a terminal, an electrically conductive sleeve secured to said terminal, an insulating sleeve within said conductive sleeve, said sleeves each having diametrically disposed apertures coaxial-with the apertures of the other sleeve, an insulating pin extending diametrically across said sleeves and disposed in said aper' tures, a strain Wire looped about said pin and disposed within said insulating sleeve, and a conductor mechanically connected to said strain Wire.

22. A link for connecting electrical terminals, said link comprising a terminal including an electrically conductive sleeve, an insulating sleeve Within said conductive Lsleeve, said insulating sleeve having a radially disposed aperture, said conductive sleeve having an indent projecting into said aperture and retaining the insulating sleeve within said conductive sleeve, a strain pin adjacent said aperture and held against withdrawal from said insulating sleeve, and a conductor mechanically connected to said strain Wire.-

' RALPH H. EARLE. 

